As described in U.S. patent application Ser. No. 09/099,293 filed Jun. 18, 1998 (now U.S. Pat. No. 6,055,447) entitled “Patient CO2 Measurement” by M. Weil et al., and other patent applications incorporated by reference herein, methods and apparatus have been developed for sampling of carbon dioxide (CO2) as present in human tissue.
Examples include measurement strategies for determining tissue CO2 by sampling gases diffused across a mucous membrane. In a further example, a system for sublingual measurement of CO2 has been made and marketed as the CapnoProbe by Nellcor Puritan Bennett (Tyco Healthcare/Mallinckrodt). Unfortunately there are challenges involved with this approach (see FDA Press Release P04-82 dated Aug. 27, 2004, which is published on the web as http://www.fda.gov/bbs/topics/news/2004/NEW01108.html).
Each such probe is packaged in a metal canister filled with a saline solution and sealed in a foil envelope labeled as non-sterile. In this instance, the probe and associated saline were reported to contain the bacteria Burkholderia Cepacia and other opportunistic pathogens that can cause serious infections, usually in persons who have decreased resistance to infection. This has resulted in the recall of certain devices. The saline storage limitations are related to the detection technology employed. See, for example, U.S. patent application Ser. No. 08/535,878 filed Sep. 28, 1995 by J. Alderete, et al. for “Optical Carbon Dioxide Sensor, and Associated Methods of Manufacture” (now U.S. Pat. No. 5,714,121 assigned to Optical Sensors Incorporated), which is incorporated by reference herein. What is needed is an inexpensive carbon dioxide sensor for reliable, and safe measurement of carbon dioxide that does not require storage in a saline solution to maintain its operational characteristics.